FI91833B - Method for producing a metal matrix composite and a metal matrix composite body obtained by the method - Google Patents

Abstract

The present invention relates to a novel method for forming metal matrix composite bodies and novel metal matrix composite bodies produced thereby. Particularly, a polycrystalline oxidation reaction product of a parent metal and an oxidant is first formed. The polycrystalline oxidation reaction product is thereafter comminuted into an appropriately sized filler material (2) which can be placed into a suitable container (4) or formed into a preform. The filler material or preform of comminuted polycrystalline oxidation reaction product (2) is thereafter placed into contact with a matrix metal alloy (1) in the presence of an infiltration enhancer, and/or an infiltration enhancer precursor and/or an infiltrating atmosphere, at least at some point during the process, whereupon the matrix metal alloy (1) spontaneously infiltrates the filler material or preform. As a result of utilizing comminuted or crushed polycrystalline oxidation reaction product, enhanced infiltration (e.g., enhanced rate or amount) is achieved. Moreover, novel metal matrix composite bodies are produced.

Description

91833

Method for producing a metal matrix composite and a metal matrix composite cap-5 obtained by the method

The present invention relates to a new method for forming metal matrix composite bodies and to products produced by the method. More specifically, a polycrystalline oxidation reaction product is first formed from the parent metal and the oxidant. The polycrystalline oxidation reaction product is then comminuted into a suitably sized filler which can be placed in a suitable container or from which a preform can be formed. The filler or preform in the comminuted polycrystalline oxidation reaction product is then contacted with the matrix alloy in the presence of an infiltration enhancer and / or infiltration enhancer precursor and an infiltration atmosphere at each step of the process, after which the matrix is spun off. As a result of the use of the comminuted or crushed polycrystalline oxidation reaction product, improved penetration (e.g., higher rate or amount) is achieved. In addition, new metal matrix composite bodies are produced.

Composite products comprising a metal matrix and a reinforcing or reinforcing phase, such as ceramic particles, fibrous crystals, fibers, or the like, look promising for many different applications because they combine some of the rigidity and wear resistance of the reinforcing phase with the ductility and formability of the metal matrix. In general, the metal matrix composite provides improvements in properties such as strength, stiffness, abrasion resistance, and retention of strength at higher temperatures compared to the matrix metal in its monolithic form, but the amount up to which a given property can be improved greatly of the ingredients involved, their volume or weight ratios, and how they are handled to form the composite. In some cases, the composite may also be lighter than the matrix metal as such. Aluminum matrix rice composites reinforced with aggregates such as silicon carbide in the form of particles, flakes or fibrous crystals are of interest due to their greater rigidity, wear resistance and high temperature strength compared to aluminum.

Various metallurgical methods for making aluminum matrix composites have been described, including methods based on powder metallurgy techniques and molten metal penetration techniques utilizing die casting, vacuum casting, mixing, and plasticizers. Using powder metallurgy techniques, the metal in powder form and the reinforcing agent in the form of powder, fiber crystals, cut fibers, etc. are mixed and then either cold-pressed and sintered, or hot-pressed. The largest ceramic volume fraction of the silicon carbide-reinforced aluminum matrix composite produced by this method has been reported to be about 25% by volume in the case of fibrous crystals and about 40% by volume in the case of particles.

The production of metal matrix composites by conventional methods using powder metallurgical techniques imposes some limitations on the properties of the products to be obtained. The volume fraction of the ceramic phase in the composite is typically limited, in the case of particles, to about 40%. By ringing, the pressing action sets the limit to the size that can be practically achieved. Only relatively simple product shapes are possible without subsequent processing (e.g. shaping or machining) or without the use of complex presses. Uneven shrinkage, as well as microstructural unevenness, due to solids separation and particle growth may also occur during sintering.

U.S. Patent 3,970,136 describes a method of forming a metal matrix composite comprising a fibrous reinforcement, e.g., silicon carbide or aluminum fiber crystals, having a predetermined fiber orientation. The composite 10 is made by placing parallel mats or blankets of planar fibers in a mold together with a source of molten matrix metal, e.g., aluminum, between at least some of the mats, and applying pressure so that the molten metal is forced to penetrate the mats and surround the directed fibers. Molten metal can be cast on top of the carpet stack, forcing it to flow between the carpets under pressure. Up to 50% by volume of the reinforcing fibers in the composite have been reported.

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The above penetration method involves surprising variations in pressure-induced flow processes. i.e., possible irregularities in matrix formation, porosity, etc., given that it depends on external pressure to force molten matrix metal through the fibrous mats. The unevenness of the properties is possible even if the molten metal is led from several points to the fibrous arrangement. Accordingly, complex mat / source-30 arrangements and flow paths must be provided for a suitable and uniform feel. to provide entanglement in the stack of nonwoven mats. The above-mentioned pressure penetration method also allows only with respect to the relatively small reinforcement and matrix volume, due to the difficulty of penetration inherent in the large mat volume. In addition, the molds must contain molten metal under pressure, which * increases the cost of the process. Finally, the aforementioned 4,91833 method, which is limited to penetration into stretched particles or fibers, is not suitable for forming aluminum matrix composites reinforced with randomly oriented particles, fibrous crystals, or fibrous materials.

In the manufacture of alumina-alumina-filled composites, aluminum does not readily wet alumina, making it difficult to form a uniform product. Various solutions have been proposed to these 10 problems. One such approach is to coat aluminum with a metal (e.g., nickel or tungsten) which is then hot pressed together with the aluminum. In another technique, aluminum is alloyed with lithium, and the alumina can be coated with silica. However, with these composites, the properties vary, or the coatings can weaken the filler, or the matrix contains lithium, which can affect the properties of the matrix.

U.S. Patent 4,232,091 overcomes some of the difficulties encountered in the art in preparing aluminum matrix alumina-filled composites. This patent describes the application of a pressure of 75 to 375 kg / cm to force molten aluminum (or molten aluminum alloy) into a fibrous or fibrous crystal mat of alumina 25 preheated to a range of 700 to 1050 ° C. The maximum ratio of alumina to metal in the resulting solid casting was 0.25: 1. Because this method relies on external pressure to effect penetration, it suffers from many of the same shortcomings as U.S. Patent 3,970,136.

EP-A-115,742 describes the preparation of alumina-alumina composites which are particularly useful as electrolyte cell components and in which the cavities of the preform alumina matrix are filled with aluminum, and for this purpose various techniques are used to wet the alumina throughout the preform. The alumina is wetted with, for example, a wetting agent or metal in titanium, zirconium, hafnium or niobium diboride, i.e. lithium, magnesium, calcium, titanium, chromium, iron, cobalt, nickel, zirconium or hafnium. An inert atmosphere such as argon is used to promote wetting. This publication also discloses applying pressure to cause molten aluminum to penetrate uncoated mat) rice. In this regard, penetration is accomplished by first evacuating the pores and then applying pressure to the molten aluminum in an inert atmosphere, e.g., argon. Alternatively, the preform may be penetrated by a vapor phase aluminum coating to wet the surfaces 15 prior to filling the cavities with penetrating molten aluminum. In order to ensure that the aluminum remains in the pores of the preform, heat treatment is required, e.g. at a temperature of 1400 to 1800 ° C, either under argon or under vacuum. Otherwise, either the exposure of the penetrated substance 20 under pressure to the gas, or the removal of the penetrating pressure, causes the aluminum to disappear from the body.

The use of wetting agents to cause the alumina component to penetrate the molten metal-containing electrolyte cell is also disclosed in EP Application 94353. This publication describes the production of aluminum by electrolysis in a cell having a current conductor cathode as a cell shell or substrate. To protect this substrate from molten cryolite, a thin coating of a mixture of wetting agent and anti-dissolution agent is applied to the alumina substrate 30 before the cell is started or when immersed in the molten aluminum produced by the electrolysis process. The wetting agents described are titanium, zirconium, hafnium, silicon, magnesium, vanadium, chromium, niobium or calcium, and titanium is preferred. Compounds of boron, carbon and nitrogen are explained to be • useful in preventing the dissolution of wetting agents in molten aluminum. However, this publication does not propose the production of metal matrix composites, nor does it suggest the formation of such composites, for example under a nitrogen atmosphere.

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In addition to the use of pressure and wetting agents, it has been described that the application of vacuum promotes the penetration of molten aluminum into the porous ceramic body. For example, U.S. Patent 3,718,441 reports penetration of a ceramic body 10 (e.g., boron carbide, alumina, and beryllium oxide) with either molten aluminum, beryllium, magnesium, titanium, vanadium, nickel, or chromium in a vacuum of less than 10 ”torr. Between 10 “...

A vacuum of 10-6 torr resulted in poor wetting of the ceramic with molten metal so that the metal did not flow freely into the ceramic cavities. However, wetting is said to be improved when the vacuum was reduced to less than 10-6 torr.

U.S. Patent 3,864,154 also discloses the use of a vacuum to effect intrusion. This patent explains the placement of a cold-pressed AlB 12 body on a bed of cold-pressed aluminum powder. Additional aluminum was then placed on top of the AlBi2 powder body. A melting vessel in which the AlBi2 body was "layered" between the layers of aluminum powder was placed in a vacuum oven. A vacuum of about 10-5 torr was provided in the furnace for degassing. The temperature was then raised to 1100 ° C where it was maintained for 3 hours. Under these conditions, molten aluminum penetrated 30 AlB 12 pieces.

U.S. Patent 3,364,976 discloses a plan to create a self-evolving vacuum in a body to increase the penetration of molten metal into the body. In particular, it is explained that a body, e.g. a graphite mold, a steel mold or a porous refractory material, is completely immersed in the molten metal. In the case of a mold, the mold cavity filled with the gas reacting with the metal li 7 91833 communicates with the molten metal on the outside through at least one opening in the mold. When the mold is immersed in the melt, the cavity is filled by the formation of a self-evolving vacuum 5 due to the reaction of the gas in the cavity and the molten metal. In particular, the vacuum is the result of the formation of a solid oxide form of the metal. Thus, this publication discloses that it is essential to effect a reaction between the gas in the cavity and the molten metal. However, the use of a mold to create a vacuum may not be desirable due to the immediate limitations associated with the use of the mold. Molds must first be machined to a specified shape; then finalized, machined to produce an acceptable casting surface in the mold; then assemble 15 before using them; then disassemble after use to remove the casting from them; and thereafter the mold must be put back into service, which would most likely involve reprocessing the mold surfaces or removing the mold if it is no longer acceptable for use. Machining a mold into a complex shape can be very expensive and time consuming. In addition, it may be difficult to remove the formed part from the complex shaped mold (i.e., the complex shaped castings may break when removed from the mold). In addition, although the publication suggests that a porous refractory could be directly embedded in molten metal without the need for a mold, the refractory should be a unitary body because there is no possibility of penetrating a loose or separated porous material without a reservoir mold (i.e., it is generally believed that the particulate matter would typically dissociate or disperse upon placement in molten metal). In addition, if it is desired to provide penetration into the particulate matter or loosely formed preform, precautions should be taken to prevent penetration. · · 8 91833 metal would displace part of the particulate matter or preform, leading to inhomogeneous microstructure.

Similarly, there has long been a need for a simple and reliable method for producing shaped metal slime rice composites that is not based on the application of pressure or vacuum (either externally applied or internally developed), or on the use of harmful wetting agents to create a metal matrix in another. such as a ceramic substance. In addition, there has long been a need to minimize the number of final machining operations required to obtain a metal matrix composite body. The present invention satisfies these needs by providing a spontaneous infiltration mechanism to provide infiltration into a substance (e.g., a ceramic) that can be formed into a preform of molten matrix metal (e.g., aluminum) in the presence of an infiltration atmosphere (e.g., nitrogen) at normal atmospheric pressure; at some stage in the process of 20.

The content of this application is related to several parallel applications. In particular, these other co-pending applications describe novel methods for producing metal matrix composite materials (hereinafter referred to in some cases as "co-metal matrix applications").

A novel method for producing a metal matrix composite material is described in our U.S. Application 049,171, entitled "Metal Matrix Composites," which is now approved in the United States. According to said invention, the metal matrix composite is produced by infiltrating a permeable filler (e.g. collected or collected with a coated material) of molten aluminum containing at least 1% by weight of magnesium and preferably at least 3% by weight of magnesium. Penetration occurs 9 91833 spontaneously without the use of external pressure or vacuum. The feed of the molten alloy is contacted with the filler mass at a temperature of at least about 675 ° C in the presence of a gas comprising about 10 to 100% by volume, preferably at least about 50% by volume of nitrogen, the remainder, if any. -oxidizing gas, e.g. argon. Under these conditions, the molten aluminum alloy penetrates the ceramic mass at normal atmospheric pressure to form an aluminum (or aluminum alloy) matrix composite. When the desired amount of filler is penetrated by the molten aluminum alloy, the temperature is lowered to solidify the alloy to form a solid metal matrix structure that encloses the reinforcing filler. Usually, and preferably, the molten mixture fed is sufficient to cause the penetration to proceed substantially within the limits of the filler mass. The amount of filler in the aluminum matrix composites produced according to application 049,171 can be very large. In this sense, volume ratios of filler to mixture of greater than 20: 1: 1 can be achieved.

In the process conditions according to the above-mentioned application 049,171, aluminum nitride can be formed as a discontinuous phase distributed throughout the aluminum matrix.

The amount of nitride in the aluminum matrix may vary depending on factors such as temperature, composition of the mixture, composition of the gas and filler. Thus, by adjusting one or more such elements of the system, certain properties of the composite can be tailored. However, for some end-use applications, it may be desirable for the composite to contain little or no aluminum nitride.

It has been found that higher temperatures promote penetration but result in a more sensitive formation of nitride in the process. The invention of 049,171 allows the selection of a balance between penetration kinetics and nitride formation.

An example of suitable barrier means for use in forming metal-5 matrix composites is described in U.S. Application 141,642, entitled "Method for Making Metal Matrix Composites Using a Barrier Agent." According to the method of the present invention, a barrier medium (e.g., particulate titanium diboride or graphite-10 material, such as a flexible graphite tape product sold by Union Carbide under the tradename Grafoil (R)) is placed at a defined filler interface and the matrix mixture penetrates the barrier-defined interface. The barrier means is used to prevent, repel, or stop the intrusion of the molten mixture of soil, thereby providing a network, or near-network, of the resulting metal matrix composite. Correspondingly formed metal matrix composite bodies have an outer shape that substantially corresponds to the inner shape of the barrier means.

The process of U.S. Patent Application 049,171 was improved by co-pending U.S. Patent Application 168,284, entitled "Metal Matrix Composites and Techniques for Making Them." According to the methods disclosed in said application, the matrix metal alloy is present as a first source of metal and as a storage source of matrix metal in communication with the first source of molten metal, for example by gravity flow. In particular, under the conditions disclosed in said application, the source of the molten matrix mixture begins to penetrate its filler mass at normal atmospheric pressure and thus begins to form a metal matrix composite. The first source of molten matrix metal is consumed as it penetrates the filler mass and, if desired, may be added, preferably in a continuous manner, from a molten matrix metal storage source as spontaneous penetration continues. When the desired amount of permeable filling! 11,91833 substance is penetrated by the molten matrix mixture, the temperature is lowered to solidify the mixture to form a solid metal matrix structure surrounding the reinforcing filler. It is to be understood that the use of a metal storage source is only one embodiment of the invention described in said patent application, and it is not necessary to combine the storage source embodiment with each of the alternative embodiments of the invention, some of which could also be useful in the present invention.

The source of metal can be present in an amount such as to provide a sufficient amount of metal to penetrate the predetermined amount of permeable filler. Alternatively, the optional barrier means may be in contact with the permeable mass of filler at least on one side thereof to define the interface.

In addition, although the amount of molten matrix mixture fed should be sufficient to allow spontaneous infiltration to proceed at least substantially to the interfaces (i.e., barrier surfaces) of the filler permeable mass, the amount of mixture in the storage source could exceed a sufficient amount to complete the infiltration. and in addition, the excess molten alloy could remain and adhere to the metal matrix composite body. Thus, when an excess of molten alloy is present, the resulting body is a complex composite body (e.g., a macrocomposite) in which the ceramic body penetrated by the metal matrix directly binds to the excess metal remaining at the storage source.

Each of the parallel metal matrix applications described above describes methods for producing metal matrix composite bodies and the new metal matrix composite bodies produced thereby.

12 91833

In addition, many co-pending patent applications and one approved patent, of which we are the holder (referred to below in some cases 5 as "co-ceramic matrix applications"), describe new methods for reliably producing ceramic materials and ceramic composites. The process is species-specifically described in our U.S. Pat. No. 4,713,360, entitled "Novel Ceramic Materials and Methods for Making Them" (cf. EP-0 155 831). This patent describes a process for producing self-supporting ceramic bodies which are grown as an oxidation reaction product of a molten precursor metal, wherein the metal is reacted with an oxidant in the vapor phase to provide an oxidation reaction product. The molten metal passes through the formed oxidation reaction product, reacting with the oxidant and thereby continuously producing a ceramic polycrystalline body, which may contain a composite metal component if desired. The process may be intensified or, in some cases, enabled by the use of one or more dopants doped in the parent metal. For example, when oxidizing aluminum in air, it is desirable to alloy magnesium and silicon with alpha alumina to produce ceramic fields.

The process of U.S. Patent 4,713,360 was improved by applying dopants to the parent metal surface, as described in our co-pending U.S. Application 822,999 based on 30 applications 776,965, which in turn is a continuation of application 747,788 based on application 632,636 entitled "Methods with Self-Supporting Ceramics". (cf. EP application 0 169 067).

35 A similar oxidation phenomenon was exploited in the production of ceramic composite bodies, as described in our co-pending U.S. Patent Application No. 819,397, No. 13,918,333, which is a continuation of Application No. 697,876 entitled "Composite Ceramic Articles and Methods for Making Them" 5 (cf. EP Application 0). 193 292). These applications describe novel methods for producing a self-supporting ceramic composite body by growing an oxidation reaction product from its parent metal precursor to a permeable filler mass (e.g., a silicon carbide particulate filler or an alumina particulate filler), by penetrating the filler, or by supporting the filler. However, the resulting composite does not have any defined or predetermined geometry, shape, or structure.

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A method for producing ceramic composite bodies having a predetermined geometry or shape is described in our co-pending application US-861,025 under the heading "Shaped ceramic composites and methods for their production" (cf. EP application 0 245 192). According to the process of this U.S. application, the evolving oxidation reaction product penetrates a permeable, self-supporting, filler (e.g., alumina or silicon carbide preform) preform toward a defined interface, resulting in a predetermined composite having a predetermined geometry.

Each of our aforementioned ceramic matrix patent applications describes methods for producing ceramic matrix composite bodies and novel ceramic matrix composite bodies produced therefrom.

As described in our ceramic matrix patent applications 35 and patents, new polycrystalline ceramic materials or polycrystalline ceramic composites are produced as a result of the oxidation reaction of a parent metal and an oxidant (e.g., solid, liquid, and / or gas). According to the 5 species-specific method described in these co-ceramic matrix patent applications and patents, the parent metal (e.g., aluminum) is heated to a high temperature above its melting point, but below the melting point of the oxidation reaction product to react with the . At this temperature, the oxidation reaction product, or at least a portion thereof, is in contact with and extends between the molten parent metal body and the oxidant, whereby the molten metal is absorbed or passed through the formed oxidation reaction product 15 toward the oxidant. The transferred molten metal forms an additional new oxidation reaction product upon contact with the oxidant, on the surface of the previously formed oxidation reaction product. As the process continues, more metal passes through the formation of this polycrystalline oxidation reaction product, thereby continuously "increasing" the ceramic structure of the interconnected crystallites. The resulting ceramic body may contain metal components, such as non-oxidized portions of the parent metal, and / or from the cavity. Oxidation is used in its broadest sense in all parallel patent matrix patent applications and patents within the scope of this application, and refers to the loss or partition of electrons between a metal and an oxidant, where the oxidant may be one or more elements and / or compounds. Similarly, elements other than oxygen 30 can act as an oxidant.

In certain cases, the parent metal may require the presence of one or more dopants to advantageously effect or allow the growth of the oxidation reaction product. Such dopants may be at least partially doped with the parent metal during or prior to the growth of the oxidation reaction product. For example, if aluminum is used as the parent metal and air is used as the oxidant, then dopants such as magnesium and silicon, to name but a few of the larger class of dopants, can be doped with aluminum and the resulting growth mixture is used as the parent metal. The oxidation reaction product resulting from such a growth mixture comprises alumina, typically alpha alumina.

Novel ceramic composite structures and methods for making cellos have also been described and claimed in the aforementioned co-pending ceramic-matrix patent applications using an oxidation reaction to produce ceramic composite structures comprising a substantially inert filler. e.g., the use of a filler that is at least partially reactive with the advancing oxidation reaction product and / or parent metal) that has penetrated the polycrystalline ceramic matrix. The parent metal is placed adjacent to a permeable filler mass (or preform) that can be shaped and processed to self-support, and is then heated to form a molten parent metal body that is reacted with an oxidant as described above to form an oxidation reaction product. As the quench reaction product grows and penetrates the adjacent filler, the molten metal is absorbed through the previously formed oxidation reaction product into the filler mass, where it reacts with the oxidant to form additional new oxidation reaction product on the surface of the previously formed oxidation reaction product. The resulting growth of the oxidation reaction product penetrates or surrounds the filler, and results in the formation of a ceramic composite structure from the polycrystalline ceramic matrix surrounding the filler. As also mentioned above, a barrier means may be used in the filler (or preform) to form a boundary or surface for the ceramic composite structure.

The process of the present invention is characterized in that a comminuted oxidation reaction feed is provided as a filler and the molten matrix metal is spontaneously infiltrated into at least a portion of the filler using an infiltration enhancer and / or an infiltration enhancer precursor and an infiltration atmosphere. the comminuted form of the oxidation reaction product provides better kinetics of penetration of the molten matrix metal into the filler or preform, and / or lower process temperatures, and / or lower likelihood and / or lower cost of metal / particle reactions, In addition, the present invention smokes higher filler volume.

Likewise, with respect to the characteristics of the metal matrix composite 20 body of the invention, reference is made to the appended claims 8-11.

Once the comminuted polycrystalline oxidation reaction product is obtained and formed in the filler or preform, then the metal matrix composite body is produced by penetrating its permeable filler mass or preform. More specifically, the infiltration enhancer and / or the infiltration enhancer precursor and the infiltration atmosphere are in contact with the filler or preform at some stage in the process to allow spontaneous infiltration of the molten matrix metal into the filler or preform. In addition, instead of the penetration enhancer precursor, the penetration enhancer can be fed directly into at least one of the preform, the filler mass, and / or the matrix mat. Finally, at least during spontaneous infiltration, the infiltration enhancer should be located at least in a portion of the filler or preform.

For example, a matrix metal (e.g., an aluminum alloy) is placed in contact with the surface of the filler mass or li 17 91833 preform (e.g., ceramic particles, fibrous crystals, and / or fibers) so that when the matrix metal is in a molten state, it can penetrate filler or preform. In addition, unless the penetration enhancer 5 or the penetration enhancer precursor itself is fed in the comminuted polycrystalline oxidation reaction product, it can be added at least to either the matrix metal or the comminuted oxidation reaction product (be it a filler or a preform). The combination of the comminuted polycrystalline oxidation-10 reaction product, the matrix metal, the penetration enhancer precursor and / or the penetration enhancer, and the combination of the penetration atmosphere causes the matrix metal to spontaneously penetrate the filler or preform.

15

It should be noted that this application mainly relates to aluminum matrix metals which are in contact with magnesium at some point during the formation of the metal matrix composite body, which acts as a precursor to the penetration enhancer 20 in the presence of a nitrogen acting as an penetration atmosphere. Thus, spontaneous infiltration occurs in the matrix metal / infiltration enhancer precursor / infiltration atmosphere system of the aluminum / magnesium / nitrogen system. However, many other matrix metal / penetration enhancer precursor / penetration atmosphere systems * may behave similarly to the aluminum / magnesium / nitrogen system. Similar spontaneous infiltration behavior has been observed in the aluminum / strontium / nitrogen system; aluminum / zinc / oxygen system; as well as in the aluminum / calcium / nitrogen system.

. Similarly, although this application is primarily concerned with the aluminum / strontium / nitrogen system, it is to be understood that other metal matrix / penetration enhancer precursor / penetration atmosphere systems may be used in a similar manner and are considered to be encompassed by the invention.

i · 18 91 833

When the matrix metal comprises an aluminum alloy, and the comminuted polycrystalline oxidation reaction product comprises a comminuted alumina polycrystalline oxidation reaction product, the aluminum alloy is contacted with a filler or preform, for example in the presence of magnesium, and / or exposed to magnesium at some point in the process. The aluminum alloy and filler or preform are maintained under a nitrogen atmosphere for at least a portion of the process. Under these conditions, spontaneous infiltration occurs in the preform or filler, and the amount or rate of spontaneous infiltration and metal matrix formation varies according to a given arrangement of process conditions, including, for example, infiltration of the system (e.g., aluminum alloy and / or preform) and / or infiltration atmosphere. magnesium) and / or the penetration enhancer concentration, the size and / or composition of the filler or preform, the nitrogen concentration in the penetration atmosphere, the time at which the penetration is allowed to occur, and / or the temperature at which the penetration occurs. Spontaneous infiltration typically occurs to such an extent that it is sufficient to completely surround the preform or filler.

25 Definitions "Aluminum" as used herein, and in connection with both ceramic matrix composite bodies and metal matrix rice composite bodies, means substantially pure metal (e.g., relatively pure, commercially available unalloyed aluminum) or other grades of metal and alloys, such as commercially available metals, containing impurities and / or containing constituents such as iron, silicon, copper, magnesium, manganese, chromium, zinc, etc. For the purposes of this definition, an aluminum alloy is an alloy or a compound of metals containing aluminum as a main ingredient.

"Remaining non-oxidizing gas" as used herein in connection with metal matrix composite bodies means that any gas in addition to the primary gas forming the penetration atmosphere is either an inert gas or a reducing gas that does not substantially react with the matrix metal under the process conditions. The amount of any oxidizing gases potentially present as an impurity in the gas (s) should be insufficient to oxidize the matrix metal to any substantial extent under the process conditions.

"Inhibitor" or "inhibitor" as used herein in connection with ceramic matrix composite bodies means any suitable substance, compound, element, composition, or the like that, under process conditions, maintains some degree of integrity, is not substantially volatile (i.e., the inhibitor does not evaporate as much). that it becomes useless as an inhibitor), and preferably permeates the oxidant in the vapor phase (if used) while being able to locally inhibit, poison, stop, interfere, etc. with the continued growth of the oxidation reaction product.

"Blocking agent" or "blocking means" as used herein in connection with metal matrix composite bodies means any suitable means for interacting, blocking, preventing or stopping the migration, migration or the like of molten matrix metal behind a filler mass or preform interface, said blocking means defining a cell barrier . Suitable barrier means can be any substance, compound, element, composition, or the like that maintains some degree of integrity under the process conditions and is not substantially volatile (i.e., the barrier does not evaporate to such an extent that it becomes useless as a barrier).

In addition, suitable "barrier means" include substances that are substantially incapable of wetting the migrating molten matrix metal during the process used. This type of barrier appears to have substantially little or no tendency to coalesce with the molten matrix metal, and the barrier means prevents or repels migration over the defined interface of the filler mass 10 or preform. The barrier reduces any final machining or grinding that may be required and defines at least a portion of the surface of the resulting metal matrix composite product. The blocking agent may in certain cases be permeable or porous, or it may be made permeable, for example by drilling holes in the blocking agent or by piercing it so that the gas comes into contact with the molten matrix metal.

"Residues" or "parent metal residues" or "mat-20 rice metal residues" as used herein refers to any portion of the original parent metal or matrix metal body that remains and is not worn during the formation of the metal matrix composite body, and typically, if allowed to cool, remains at least 25 pieces formed in partial contact. It should be understood that residues may also typically contain some oxidized components of the parent metal or matrix metal and / or another or foreign metal.

30 "Ceramic" as used herein should not be limited to a ceramic body in its classical sense, i.e., in the sense that it is composed entirely of non-metallic and inorganic materials, but means a body that is substantially ceramic in structure or in terms of its properties, although the part may contain small or significant amounts of one or more metal constituents (insulated and / or)! 21,91833 associated, depending on the process conditions used to form the article), which date from the parent metal, or are reduced from an oxidant or dopant, most typically in the range of about 1 to 40% by volume, but may contain more metal.

"Dopant" as used herein in connection with ceramic matrix composite bodies means substances (components of the mixture 10 or components together and / or incorporated and / or in or on a filler) which, when used with a parent metal, favorably affect or promote the oxidation reaction process and / or modify the growth process. to alter the microstructure and / or properties of the product. While not wishing to be bound by any particular theory or explanation of the operation of dopants, it appears that some dopants are useful in promoting the formation of an oxidation reaction product in cases where there is no naturally occurring surface energy relationship between the parent metal and its oxidation reaction product to promote such formation. The dopants can: form preferred surface energy ratios that promote or cause wetting of the oxidation reaction product with molten parent metal; forms a "precursor layer" on the growth surface by reacting with a mixture, oxidant and / or filler which a) minimizes the formation of a protective and uniform oxidation reaction product layer (s), b) can promote the solubility (and thus penetrability) of the oxidant in molten metal, and / or c) allowing the oxidant to pass from the oxidizing atmosphere through any of the precursor oxide layers to then combine with the molten metal to form a second oxidation reaction product; ai-35 induces structural changes in the myrostructure in the oxidation reaction product as it is formed or thereafter; altering the composition and properties of the metal components of such an oxidation reaction product; and / or promotes the formation of growth crystal embryos and the uniformity of growth of the oxidation reaction product »5" Filler "as used herein in connection with both ceramic matrix bodies and metal matrix composite bodies is intended to contain either individual materials or mixtures of substances substantially unreactive to metal (e.g. parent metal) and / or oxidation 10 and / or have limited solubility in metal (e.g. parent metal) and / or oxidation reaction product, and may be single or multi-phase. The fillers can be arranged in a number of different forms, such as powders, strips, flakes, microspheres, fiber crystals, bubbles, etc., and can be either dense or porous. The filler may also include ceramic fillers such as alumina or silicon carbide in the form of fibers, cut fibers, particles, fibrous crystals, bubbles, spheres, nonwovens, or the like, and ceramic coated fillers such as carbon fibers coated with carbon oxide or coated with alumina. the corrosive effect of molten parent metal-aluminum. The fillers may also comprise metals.

"Growth mixture" as used herein in connection with both ceramic matrix composite bodies and metal matrix composite bodies means a mixture that initially contains or at some point in the process obtains a sufficient amount of the required ingredient to result in an increase in the oxidation reaction product.

"Penetration atmosphere" as used herein in connection with metal matrix composite bodies means the atmosphere present and interacting with the matrix metal and / or preform (or filler) and / or the penetration enhancer precursor and / or penetration enhancer and / or penetration enhancer. allows or promotes the occurrence of spontaneous infiltration of matrix metal.

"Penetration enhancer" as used herein in connection with metal matrix-5 composite bodies means an agent that promotes or assists spontaneous penetration of matrix metal into a filler or preform. The infiltration enhancer can be formed, for example, by the reaction of the infiltration enhancer precursor with the infiltration atmosphere to 1) 10 gases and / or 2) the infiltration enhancer precursor and the infiltration atmosphere reaction product and / or 3) the infiltration enhancer precursor and filler. In addition, the penetration enhancer may be fed directly to at least one of the following: a preform, and / or a matrix metal, and / or an infiltration atmosphere; and it may function in substantially the same manner as an infiltration enhancer formed by the reaction of a precursor of the infiltration enhancer with another agent. Finally, at least during spontaneous infiltration, the infiltration enhancer should be located in at least a portion of the filler or preform to effect spontaneous infiltration.

"Penetration enhancer precursor" as used herein in connection with metal-25 matrix composite bodies means a substance which, when used in conjunction with a matrix metal, preform and / or infiltration atmosphere, forms an infiltration enhancer that causes or assists spontaneous infiltration of the matrix metal into the filler. Without wishing to be bound by any particular theory or explanation, it appears that the intrusion promoter precursor should be able to be located, located, or transported to a location that allows the intrusion promoter precursor to interact with the intrusion atmosphere and / or preform or metal or with. For example, in some matrix metal / infiltration enhancer precursor / infiltration atmosphere systems, it is desirable for the infiltration enhancer precursor to vaporize at a temperature at which the matrix metal melts, near this temperature, or in some cases even slightly above this temperature. Such evaporation may result in: 1) a reaction of the infiltration enhancer precursor with the infiltration atmosphere to form a gas that promotes wetting of the filler or preform with the matrix metal; and / or 2) reacting the infiltration enhancer precursor with the infiltration atmosphere to form an infiltration enhancer in the form of a solid, liquid or gas at least in a portion of the filler or preform that promotes wetting; and / or 3) a reaction of the penetration enhancer precursor in the filler or preform to form a solid, liquid or gaseous penetration enhancer in at least a portion of the filler or preform that promotes wetting.

"Liquid phase oxidant" or "liquid oxidant" as used herein in connection with ceramic matrix composite bodies means an oxidant in which the indicated liquid is the sole, predominant, or at least significant oxidant of the parent or precursor metal under the process conditions.

25

Reference to a liquid oxidant means one that is a liquid under the conditions of an oxidation reaction. Similarly, the liquid oxidant may have a solid precursor, such as a salt, that melts under the conditions of the oxidation reaction. Alternatively, the nes-30 oxidizer may have a liquid precursor (e.g., a solution of the agent) used to saturate a portion or all of the filler and that melts or decomposes under the conditions of the oxidation reaction to produce a suitable portion of the oxidant. Examples of liquid oxidants as defined herein include low melting glass.

li 25 91833

If the liquid oxidant is used in conjunction with a parent metal and a filler, then typically the entire bed of filler or the portion containing the desired ceramic body is impregnated with an oxidant (e.g., by coating or dipping in an oxidant).

"Matrix metal" or "matrix metal alloy" as used herein in connection with metal matrix composite bodies means the metal used to form the metal matrix-10 composite (e.g., prior to penetration) and / or the metal that mixes with the filler to form the metal matrix composite body (e.g., penetration). When a designated metal is designated a matrix metal, it is to be understood that such a matrix metal includes that metal as a substantially pure metal, a commercially available metal having impurities and / or alloying elements, a compound of metals, or an alloy in which this metal is a major component.

"Matrix metal / infiltration enhancer precursor / infiltration atmosphere system" or "spontaneous system" as used herein in connection with metal matrix composite bodies refers to a combination of substances that exhibit spontaneous infiltration into a preform and filler. It is to be understood that when the "/" sign occurs between the matrix metal of the example, the penetration enhancer precursor, and the penetration atmosphere, it is used to denote a system or combination of agents that, when combined in a certain manner, exhibits spontaneous penetration into a preform or filler.

"Metal matrix composite" or "MMC" as used herein in connection with metal matrix composite bodies means a substance comprising a two- or three-dimensionally bonded alloy or matrix metal containing a preform or filler. The matrix metal may contain various alloying elements which provide the desired mechanical and physical properties in the resulting composite.

5 "Aberrant" metal in the context of ceramic matrix composite bodies and / or metal matrix composite bodies means a metal that does not contain the same metal as the matrix metal or parent metal as the main component (for example, if aluminum is the major component of the matrix metal or parent metal), " "the main part of the metal could be, for example, nickel).

A "nitrogen-containing gas oxidant" as used herein in connection with metal matrix-15 composite bodies is a specified gas or vapor in which nitrogen is the sole, predominant, or at least significant oxidant of the parent or precursor metal under the oxidizing conditions used.

"Oxidant" as used herein in connection with metal matrix composite bodies means one or more electron acceptors or electron splitters, and may be a solid, liquid, or gas, or a combination thereof (e.g., solid and gas) under oxidation reaction conditions.

Typical oxidants include, without limitation, oxygen, nitrogen, halogen, sulfur, phosphorus, arsenic, carbon, boron, selenium, tellurium, and / or compounds and combinations thereof, for example, silica or silicates (oxygen source), methane, ethane, propane, acetylene, ethylene, propylene (hydrocarbon as a carbon source), and mixtures such as air, H2 / H2O and CO / CO2 (oxygen source), the latter two (i.e. H2 / H2O and CO / CO2) being useful in reducing ambient oxygen activity .

"Oxidation reaction product" as used herein in connection with metal matrix composite bodies means one or more metals in an oxidized state in which 27,91833 metal (s) have donated electrons or shared electrons with another element, compound, or combination thereof. Accordingly, within the scope of this definition, an "oxidation reaction product" includes the product of the reaction of one or more metals with one or more oxidants.

An "oxygen-containing gaseous oxidant" as used herein in connection with ceramic matrix composite bodies is a specified gas or vapor in which oxygen is the sole, predominant, or at least significant oxidant to the parent or precursor metal under the oxidizing conditions used.

"Base metal" as used herein in connection with ceramic matrix composite articles means the metal (s) (e.g., aluminum, silicon, titanium, tin, and / or zirconium) that is a precursor to the polycrystalline oxidation reaction product and contains this metal (s) substantially. as a pure metal, as a commercially available metal containing impurities and / or dopants, or a mixture in which the precursor of this metal is the main constituent. When a particular metal is mentioned as a parent or precursor metal (e.g., aluminum, etc.), the indicated metal should be read when read in accordance with this definition 25, unless the context indicates otherwise.

"Preform" or "permeable preform" as used herein in connection with ceramic matrix composite bodies and metal matrix composite bodies means a porous filler or filler mass made at at least one interface that substantially defines a well-penetrating matrix metal, and freshening the grain so as to provide dimensional stability before the matrix metal penetrates it. The mass should be sufficiently porous to allow matrix metal .. to spontaneously penetrate it. Typically, the preform 28 91 833 comprises a bonded group or filler arrangement, either homogeneous or inhomogeneous, and may comprise any suitable material (e.g., ceramic and / or metal particles, powders, fibers, fibrous crystals, etc., and any combination thereof). The preform can be either separate or assembled.

"Stock source" or stock, as used herein, means a separate piece of parent metal or matrix metal 10 positioned relative to a filler mass or preform so that as the metal melts, it can flow to replace, or in some cases initially provide and subsequently supplement, the parent metal or matrix metal portion; or a source that contacts the filler or preform and that penetrates or reacts to form an oxidation reaction product. The stock source can also be used to provide a metal that is different from the matrix metal.

"Second or foreign metal" as used herein in connection with ceramic matrix composite bodies or metal matrix composite bodies means any suitable metal, combination of metals, alloys, intermetallic compounds, or a source of any of these that is or is desired to be formed into a ceramic matrix. - or as part of the metal component of a metal matrix composite body instead of, in addition to or in combination with the non-oxidizing components of the parent metal. This definition includes intermetallic compounds, mixtures, solid solutions or the like formed between a parent metal and another metal.

"Solid phase oxidant" or "solid oxidant" as used herein in connection with ceramic matrix composite bodies means 35 oxidants in which the indicated solid is the sole, predominant, or at least significant base or precursor metal oxidant used under the oxidizing conditions 29,91833 sa. When a solid oxidant is used in conjunction with a parent metal and a filler, it is usually dispersed throughout the filler bed or the portion of the pdin where the oxidation reaction product grows, with the solid oxidant having, for example, 5 particles mixed with the filler or a coating with filler particles. Thus, any suitable solid oxidant may be used, including elements such as boron or carbon, or reducing compounds such as silica or certain borides having less thermodynamic stability than the result of the boride reaction of the parent metal. For example, when boron or reducing boride is used as a solid oxidant with an aluminum parent metal, the resulting oxidation reaction product comprises aluminum boride.

15

In some cases, the oxidation reaction of the parent metal with the solid oxidant may proceed so rapidly that the oxidation reaction product tends to melt due to the heat generating nature of the process. Such an event can impair the homogeneity of the microstructure of the 20 ceramic bodies. Such a rapid exothermic reaction can be enhanced by mixing in the composition a relatively inert filler that absorbs excess heat. An example of such a suitable inert filler is one that is identical or substantially identical to the intended oxidation reaction product.

"Spontaneous infiltration," as used herein in connection with metal matrix-si composite bodies, means the infiltration of a permeable filler mass or preform into a matrix of rice metal that occurs without the use of pressure or vacuum (neither externally applied nor internally developed).

35 "Vapor phase oxidant" as used herein in connection with ceramic-rice composite bodies indicates that .. the oxidant contains or comprises a specified gas or vapor, 30 91833 and denotes an oxidant in which the indicated gas or vapor is the sole, predominant or at least significant parent or precursor metal. under the oxidizing conditions used as the oxidant. For example, although nitrogen is the major component of air, the oxygen content of air is the only oxidant in the parent metal because oxygen is a much stronger oxidant than nitrogen. As a result, air falls within the definition of an "oxygen-containing gaseous oxidant" but not within the definition of a "nitrogen-containing gaseous oxidant" (for example, a "nitrogen-containing gaseous oxidant" is a process gas typically containing about 96% by volume nitrogen and about 4% by volume hydrogen). as these terms are used in the claims.

The following figures are provided to aid in the understanding of the invention, but are not intended to limit the scope of the invention. The same reference numerals have been used, where possible, in all figures to indicate corresponding parts. In the drawing: 20

Figure 1 is a schematic cross-section of an arrangement of materials used to produce the ceramic composite body of Example 1; Figure 2 is a schematic cross-section of an arrangement of materials used to produce the metal matrix composite body of Example 1; and Figure 3 is a photomicrograph at 400x magnification of a section of a metal matrix rice composite body formed in accordance with Example 1.

To form a ceramic or ceramic composite body that must be comminuted according to the method of the present invention (i.e., forming a filler or preform for use in forming a metal matrix composite body 31,91833), a parent metal (i.e., a growth alloy) that may be alloyed as below. will be explained in more detail, formed into an ingot, ingot, rod, plate or the like, and placed in an inert bed, 5 crucible or other refractory container. The parent metal may comprise one or more bodies, ingots, or the like, and may be suitably shaped in any suitable manner. The parent metal can be oxidized in conjunction with an alloying agent (described in more detail below). The permeable mass of filler, or in a preferred embodiment, a permeable, shaped preform (described in more detail below) is made to have at least one defined interface and to be permeable to the vapor phase oxidant 15 when used alone or in combination with another vapor phase oxidant. with an oxidant, and so that it is permeable to the penetrating oxidation reaction product when a permeable mass is used, whereby the parent metal can be placed on top of said permeable mass. Alternatively, the preform is placed proximally, and preferably in contact with at least one surface or at least a portion of the surface of the parent metal, such that at least a portion of the defined interface of the preform is located predominantly at, or outwardly spaced from, the parent metal surface. Preferably, the preform contacts the surface of the parent metal; but if desired, the preform may be partially immersed but not completely immersed in the molten metal. Complete immersion would cut off or block the entry of the vapor phase oxidant into the preform, thus preventing the proper development of the oxidation reaction product containing the preform. However, when a vapor phase oxidant is not used (i.e., the only oxidant used in the process is a solid oxidant or a liquid oxidant), complete immersion of the preform in the molten parent metal provides a useful alternative. Oxidation reaction product formation occurs in the direction of the defined interface. The arrangement of base metal and permeable mass or preform is placed in a suitable container, such as a boat formed of alumina or a castable refractory, and placed in an oven. The furnace atmosphere may contain an oxidant to allow vapor phase oxidation of the molten parent metal. The furnace is then heated to process conditions. In addition, electric heating is typically used to achieve the temperature used in connection with the invention. However, any heating means which can increase the oxidation reaction and melt the matrix metal and which does not adversely affect it is acceptable for use in the present invention.

A preform useful in making a composite body when at least one oxidant is a vapor phase 15 oxidant is one that is sufficiently porous, i.e., permeable, to allow the vapor phase oxidant to penetrate the preform to contact the parent metal. The preform should also be self-supporting and sufficiently permeable to allow the oxidation reaction product to develop, i.e., grow into a matrix in the preform without disturbing, interfering with or otherwise substantially altering the structure or geometry of the preform.

A solid, liquid or vapor phase oxidant 25 or a combination of such oxidants may be used. Typical oxidants include, without limitation, oxygen, nitrogen, halogen, sulfur, phosphorus, arsenic, carbon, boron, selenium, tellurium, and / or compounds and combinations thereof, e.g., silica (oxygen source), methane, ethane, propane, acetylene, ethylene, propylene (as carbon sources), and mixtures such as air, H2 / H2O, and CO / CO2 (oxygen source), the latter two (i.e., H2 / H2O and CO / CO2) being useful in reducing ambient oxygen activity. Accordingly, the oxidation reaction product 35 may comprise one or more of the following: alumina, aluminum nitride, silicon carbides, silicon boride, aluminum boride, titanium nitride, zirconium nitride, titanium boride, zirconium boride, titanium carbide, zirconium carbide, silicon triide. Although the oxidation reaction is usually explained using a vapor phase oxidant, either alone or with another oxidant which is a solid or a liquid under process conditions, it is to be understood that a vapor phase oxidant need not necessarily be used to produce the ceramic matrix composite body. When a vapor phase oxidant is not used and a solid or liquid oxidant under process conditions 10 is used, the preform need not be permeable to the ambient atmosphere. However, the preform should still be sufficiently permeable to allow the oxidation reaction product to form, i.e., grow as a matrix within the preform without disturbing, reversing, or otherwise substantially altering the preform or geometry of the preform.

The use of solid or liquid oxidants can create an environment in the preform that is more favorable to the oxidation kinetics of the parent metal than the environment outside the preform. This improved environment is useful in promoting matrix development in the preform to the limits and minimizing excessive growth. When a solid oxidant is used, it may be dispersed in the entire preform or a portion of the preform near the parent metal, such as in a particle form and mixed with the preform, or it may be used as a coating on the preform-forming particles. Suitable solid oxidants may comprise suitable elements, such as boron or carbon, or reducing compounds, such as silica (as a source of oxygen) or certain borides, which have less thermodynamic stability than the result of the boride reaction of the parent metal.

If a liquid oxidant is used, it can be dispersed throughout the preform or a portion of the preform near the molten parent metal. Reference to a liquid oxidant means one that is .. a liquid under the conditions of the oxidation reaction, and thus the liquid oxidizer may have a solid precursor, such as a salt, that melts under the conditions of the oxidation reaction. Alternatively, the liquid oxidant may have a liquid precursor (e.g., a solution of the agent) used to coat the porous surfaces of the preform or a portion thereof, and which melts or decomposes under the conditions of the oxidation reaction to produce a suitable proportion of oxidant. Examples of liquid oxidation as defined herein include low melting glasses.

As explained in our said patent applications and patents, the addition of dopants, for example in the case of an aluminum parent metal, can advantageously promote the oxidation reaction process. The effect or effects of the dopant may depend on many factors in addition to the dopant 15 itself. These factors include, for example, the desired end product, the particular combination of dopants using two or more dopants, the use of externally added dopants with the dopants, the concentration of the dopant (s), the oxidizing environment, and the process conditions.

The alloying agent or agents used in connection with the parent metal may be 1) arranged as alloying elements of the parent metal, 2) applied to at least a portion of the parent metal surface, e.g. by spraying or painting, 3) added to a filler, or any combination of methods 1), 2) and 3) . Doped mixture

for example, the dopant may be used with an externally applied dopant. The dopant source may be provided by either placing the dopant powder or a solid dopant body in contact with at least a portion of the parent metal surface. For example, a thin glass plate containing silicon can be placed on the surface of an aluminum parent metal. When an aluminum parent metal (which may be internally doped with magnesium) coated with a silicon-containing material is heated in an oxidizing environment (e.g., in the case of aluminum in air, about 850 ° C to 1450 ° C

to 35,91833, preferably about 900 ° C to 1350 ° C), growth of the polycrystalline ceramic occurs. In the case where the dopant is applied externally to at least a portion of the surface of the aluminum parent metal, the polycrystalline alumina structure generally grows substantially past the dopant layer (i.e., deeper than the applied dopant layer). In any case, one or more dopants may be applied externally to the surface of the parent metal. In addition, any concentration errors of the dopants doped with the parent metal 10 can be corrected by the additional concentration of the corresponding dopant (s) applied from outside the parent metal.

Suitable dopants for the aluminum parent metal, especially when air is the oxidant, include, for example, magnesium, zinc and silicon, in combination with each other or in combination with the other dopants mentioned below. These metals, or a suitable source of metals, can be alloyed with an aluminum-based parent metal, each concentration being about 0.1 to 10% by weight of the total weight of the resulting alloyed metal. The concentration range of each dopant depends on such factors as the combination of dopants and the process temperature.

25

Other alloying agents that are effective in promoting the growth of alumina polycrystalline oxidation reaction products with aluminum parent metal systems include, for example, germanium, tin, and lead, especially when used with magnesium. One or more such other dopants, or suitable sources thereof, are doped into an aluminum parent metal system, each concentration being about 0.5 to 15 weight percent of the total alloy; however, more desirable growth kinetics and growth morphology are achieved with dopant concentrations in the range of about 1-10% by weight of the total weight of the parent metal alloy. The alloying lead 36 91833 is generally alloyed with an aluminum-based parent metal at a temperature of at least 1000 ° C to compensate for its low solubility in aluminum; the addition of other dopants, such as tin, generally increases the solubility of lead 5 and allows the addition of dopants at lower temperatures.

When the base metal is aluminum and the oxidant is air, particularly useful dopant combinations include a) magnesium and silicon, b) magnesium, zinc and silicon. In such examples, the preferred concentration of magnesium is in the range of about 0.1 to 3 weight percent, for zinc in the range of about 1 to 6 weight percent, and for silicon in the range of about 1 to 10 weight percent.

15

Other examples of dopants useful in connection with the aluminum parent metal include sodium and lithium, which must be used individually or in combination with one or more other dopants, depending on the conditions of the process. Sodium and lithium can be used in very small amounts (in the range of parts per million, or ppm, typically about 100 to 200 ppm), and both can be used alone or in combination with another dopant (s). Calcium, boron, phosphorus, yttrium, and rare earth elements such as cerium, lanthanum, praseodymium, neodymium, and samarium are also useful dopants, and in this sense again used in conjunction with other dopants.

When applied externally, alloying agents are generally applied to a portion of the parent metal surface as a uniform coating. The amount of dopant affects a large range in relation to the amount of parent metal to which it is applied, and in the case of aluminum, experiments have not shown any upper or lower functional limit. For example, when silicon in the form of silica is used as an externally applied dopant for an aluminum-based parent metal, using li 37 91 833 air or oxygen as an oxidant, amounts as low as 0.00003 g of silicon per gram of parent metal, or about 0.0001 g of silicon bare, have been used to produce the polycrystalline per square centimeter of parent metal, together with another source of magnesium dopant. It has also been found that a ceramic structure can be provided with an aluminum-silicon alloy parent metal using oxygen as an oxidant and using MgO as an alloying agent in an amount exceeding about 0.0008 g Mg per gram of oxidizable parent metal and exceeding 0.003 g Mg per square centimeter of parent metal surface. MgO is applied.

When the parent metal is aluminum internally doped with magnesium and the oxidizing medium is air, i.e. oxygen, it has been found that magnesium is at least partially oxidized from the alloy at temperatures between about 820 and 950 ° C. In the case of such magnesium alloyed systems, magnesium forms a magnesium oxide 20 and / or a magnesium aluminate-Spinelli phase on the surface of the molten aluminum alloy and during the growth process such magnesium compounds remain mainly in the original oxide surface of the parent alloy (e.g. "starting surface"). Such purchased systems of magnesium se 25 thus provide an alumina-based structure in addition to the relatively thin layer of magnesium aluminate Spinelli on the starting surface. If desired, this starting surface can be easily removed, for example, by grinding, machining, polishing and sandblasting before using the polycrystalline ceramic product.

In an alternative embodiment of the invention, a different vapor phase oxidant may be introduced during the growth of the polycrystalline oxidation reaction product. In this context, "different" should be understood as having such ·; a composition chemically different from the original „91833 38 vapor (or solid) phase oxidant. Thus, a second oxidation reaction product formed with a "different" vapor phase oxidant results in the formation of two ceramic bodies or phases which are inextricably linked to each other and which have progressively changing properties (e.g. a second layer may form on top of the first ceramic composite body). ).

In another embodiment, the ceramic composite body 10 is first completely formed, and then the fully formed ceramic composite body is exposed to an oxidant, preferably a "different" oxidant than that used to form the oxidation reaction product that acts as a matrix of surrounded filler in the ceramic composite body. In this alternative embodiment, the residual composite parent metal in the ceramic composite body is absorbed toward at least one surface of the ceramic composite body and is reacted with a "different" oxidant to form a different oxidation reaction product on the substrate formed by the first formed oxidation reaction product.

In another embodiment of the invention, the metal component of the ceramic composite body 25 can be customized by changing its composition. More specifically, for example, another metal may be alloyed or diffused into the parent metal, for example during the growth of the oxidation reaction product, to advantageously alter the composition of the parent metal, and thus the mechanical, electrical and / or chemical properties.

To assist in the formation of the shaped ceramic composite body, a barrier means may be used in conjunction with the filler 35 or preform. More specifically, the inhibitory means useful in the present invention may be any means that interferes with, inhibits, or terminates the growth or development of the oxidation reaction. * Suitable inhibitory means may be any substance, compound, element, composition, or the like which under process conditions maintains some degree of integrity, is not volatile, and is preferably permeable to the vapor phase oxidant if a vapor phase oxidant is used, while being capable of locally preventing, poisoning, arresting, interfering, etc., the continued growth of oxidation reaction products.

10 It appears that one category of barrier means is the category of substances which the transferred parent metal may not be able to moisten. This type of inhibitor appears to have little or no affinity for the molten metal, and growth is stopped or inhibited by the inhibitor.

15 Other inhibitors tend to react with the transferred parent metal to prevent continued growth, either by dissolving or diluting the transferred metal very much or by forming solid reaction products (e.g., intermetallic compounds that interfere with the molten metal transition process). The inhibitor of this type may be a metal or an alloy, including any suitable precursors thereof, such as an oxide or a reducing metal compound, or a dense ceramic. Due to the nature of inhibiting or inhibiting growth with this Tapai-25 inhibitor, growth may extend somewhat past the inhibitor before growth ceases. However, the precursor reduces the potential for final machining and grinding that may be required with the oxidation reaction product formed. As mentioned above, the barrier agent should preferably be permeable or porous, and when using a solid, impermeable wall, the barrier agent should be open in at least one zone or at one or both ends so that the vapor phase oxidant can contact the molten parent metal.

35

Suitable inhibitors that are particularly useful in this invention when using aluminum base metals and using air as the oxidant include calcium sulfate, calcium silicate, and tricalcium phosphate. These inhibitors appear to react locally with the evolving oxidation reaction product to form an impermeable layer of calcium aluminate that locally stops more growth of the oxidation reaction product. Such inhibitors can typically be applied as a slurry or paste to these surfaces of the filler bed, which is preferably preformed into a preform. The barrier means may also contain 10 suitable combustible or volatile substances which are removed on heating, or a substance which decomposes on heating, so as to increase the porosity of the barrier means and 1 suitable combustible or volatile substance which is removed on heating, or a substance which decomposes on heating, that increasing the porosity and permeability of the barrier means. In addition, the barrier means may contain a suitable refractory particulate material to reduce any shrinkage or cracking that might otherwise occur during the process. Such a particulate material is particularly desirable having substantially the same coefficient of expansion as the bed of filler. For example, if the preform comprises alumina and the resulting ceramic comprises alumina, the blocking agent may be mixed with an alumina dihydrogen, preferably having a mesh size of about 20 to 1000 (mesh = number of screen openings per inch).

The alumina particulate material may be mixed with, for example, potassium sulphate in a ratio ranging from about 10: 1 to 1:10, with a preferred ratio of about 1: 1. In one embodiment of the invention, the barrier means comprises calcium sulphate (i.e. gypsum mortar and Portland cement. Portland cement may be mixed with gypsum mortar in a ratio of 10: 1 to 1:10, with a preferred ratio of Portland cement to gypsum mortar of about 1: 3. Portland cement alone can also be used).

35

Another embodiment, using an aluminum parent metal and air as the oxidant, involves the use of a stoichiometrically mixed gypsum plaster as a barrier, but there may also be an excess of gypsum. During the treatment, the gypsum and silica react to form calcium silicate, which results in a particularly useful inhibitor which is substantially free of cracks. In another embodiment, the gypsum mortar is mixed with about 25 to 40 weight percent calcium carbonate. When heated, the calcium carbonate decomposes and emits carbon dioxide, which increases the porosity of the barrier.

10

Other particularly useful inhibitors for aluminum-based parent metal systems include ferrous materials (e.g., a stainless steel vessel), chromium oxide, and other refractory oxides that can be used as a wall or vessel over a filler bed or as a surface layer for a filler bed. Other inhibitors include dense, sintered or fused ceramics such as alumina. These inhibitors are usually impermeable and are therefore specifically made to either allow porosity or require an open cut, such as an open end. The blocking means may form a brittle product under the reaction conditions and may be removed, for example, by grinding, to recover the ceramic body.

25

The barrier means may be made or produced in any suitable shape and size, and is preferably permeable to the vapor phase oxidant. The barrier means may be applied or utilized as a film, paste, slurry, permeable or impermeable sheet or sheet, or a reticulated or perforated web, such as a metal or ceramic filter or fabric, or a combination thereof. The blocking means may also comprise a filler and / or a binder.

35

The size and shape of the barrier means depends on the ceramic product: the desired shape. By way of example only, if the barrier line 42 91 833 is located or located at a predetermined distance from the parent metal, growth of the ceramic matrix would cease or be blocked locally where it encounters the barrier means. The shape of the ceramic product is generally inversely related to the shape of the barrier means. For example, if the concave inhibitor is at least partially spaced from the parent metal, then the polycrystalline growth occurs in the volume defined by the interface of the concave inhibitor and the surface of the parent metal. Growth ends with a substantially concave inhibitor.

After the barrier means is removed, a ceramic body having at least a convex portion defined by the concavity of the barrier means remains. It should be noted that for a barrier device with porosity, there may be some overgrowth of the polycrystalline material through the interstices, although such overgrowth is severely limited or eliminated by more effective barrier agents. In such a case, after removal of the barrier means from the grown polycrystalline ceramic body, any polycrystalline overgrowth can be removed from the ceramic body 20 by grinding, sandblasting or the like so as to provide the desired ceramic part free of polycrystalline overgrowth. To illustrate, a barrier means spaced from the parent metal and having a cylindrical protrusion in the metal direction produces a ceramic body in which the cylindrical recess inversely reproduces the diameter and depth of the cylindrical protrusion.

In order to minimize or eliminate overgrowth of the polycrystalline material in the formation of the ceramic composite, the barrier means may be placed on or in close proximity to a defined interface of any filler bed or preform. Placing the barrier means on the defined interface of the bed or preform can be accomplished in any suitable manner, such as: by depositing the barrier means on the defined interface.

Il 43 91833

Such a barrier means may be applied by painting, dipping, screen printing, vaporizing or otherwise applying the barrier in the form of a liquid, slurry or paste, or by sputtering a vaporizable barrier means, or simply by applying a layer of solid particulate barrier means, or by applying defined interface. When the barrier means is in place, the growth of the polycrystalline oxidation reaction product ends when it reaches the defined interface of the 10 preforms and contacts the barrier means.

In a preferred embodiment, to make a ceramic matrix composite body, a permeable shaped preform (described in more detail below) is formed having at least one defined interface, and wherein at least a portion of the defined interface has, or is superimposed on, a barrier means. It is to be understood that the term "preform" may include an assembly of separate preforms 20 that eventually bind to form a unitary composite. The preform is placed near and in contact with the surface of one or more parent metals such that at least a portion of the defined interface with the blocking means is located substantially distant or outward from the metal surface, and oxidation reaction product formation occurs toward the preform and toward the interface. The permeable preform is part of the assembly, and when heated in the furnace, the preform and parent metal are subjected to, or surrounded by, a vapor phase oxidant that can be used in conjunction with a solid or liquid oxidant. The metal and oxidant react, and the reaction process continues until the oxidation reaction product has penetrated the preform and comes into contact with the defined interface with or on which the barrier means is placed.

35 Most typically, the boundaries of the preform and the polycrystalline matrix substantially coincide; but on the surface of the preform: the individual components may be exposed, or they may protrude from the matrix 91833 44, as a result of which penetration and surrounding may be incomplete in the sense that the matrix completely surrounds or encloses the preform. The inhibitory agent inhibits or stops growth when in contact with the inhibitory agent, and substantially no overgrowth of the polycytic agent occurs. The resulting ceramic composite product includes a preform through which it is penetrated or is surrounded by a ceramic matrix substantially comprising a base metal and an oxidant oxidation reaction product, and optionally further one or more metal components such as non-oxidized parent metal components or reduced oxidant components. Generally, the oxidation reaction continues for as long as it is sufficient to deplete the parent metal source. The residue is removed, for example, by striking with a hammer to provide a ceramic or ceramic composite body.

After the ceramic or ceramic composite body is formed, it must then be comminuted before being used as a filler to form a metal matrix composite body. In particular, in the practice of the present invention, the polycrystalline oxidation reaction product is ground, comminuted, etc., and formed into a filler mass, or more preferably, from a filler to a preform. The ceramic or ceramic composite body can be comminuted in various ways, such as with a jaw crusher, impact mill, spindle crusher, or other conventional means, depending primarily on the desired particle size used in the metal matrix composite body.

30 The ground ceramic material is sorted by sieving and recovered for use as a filler or preform. It may be desirable to first crush the ceramic body into larger pieces of about 6-12 mm in size, for example with a jaw crusher, hammer mill, etc.

35 These large pieces could then be ground into finer particles, for example to a size of 50 mesh or finer, for example in a ball mill, impact mill, and the like.

45 9 1 8 3 3

The particulate material can then be screened to obtain fractions of the desired size. Suitable fillers may range in size from about -200 mesh to about 500 mesh, or finer, depending on the ceramic composite to be made (e.g., the intended use of the metal matrix composite body to be formed).

Once the comminuted oxidation reaction product has been obtained for the filler to the desired particle size, or shaped into a preform, the matrix metal must be made to penetrate the filler or preform.

In order to effect spontaneous infiltration of the matrix metal into the preform, a spontaneous infiltration enhancer should be provided in the spontaneous system. The infiltration enhancer could consist of a precursor of the infiltration enhancer, which could be arranged 1) in the matrix metal, and / or 2) in the preform, and / or 3) from an external source to the spontaneous system. In addition, instead of the infiltration enhancer precursor, the infiltration enhancer can be fed directly to at least one of the preform, and / or the matrix metal, and / or the infiltration atmosphere. Finally, at least during spontaneous infiltration, the infiltration enhancer should be located in at least a portion of the filler or preform.

25

In a preferred embodiment, it is possible that the infiltration enhancer precursor may be at least partially reacted with the infiltration atmosphere so that the infiltration enhancer may be formed in at least a portion of the preform before or substantially simultaneously when the preform contacts the matrix metal, e.g., if the infiltration enhancer nitrogen in the atmosphere.

35 An example of a matrix metal / infiltration enhancer precursor / infiltration atmosphere system is the aluminum / magnesium / nitrogen system. In particular, the aluminum matrix metal can be placed in a suitable refractory vessel, such as an alumina boat, which under the process conditions does not react with the aluminum matrix metal and / or filler when the aluminum is melted. The preform material can then be contacted with the molten aluminum matrix metal. In addition, instead of feeding the infiltration enhancer precursor, the infiltration enhancer can be fed directly to at least one of the preform and / or the matrix metal and / or the infiltration atmosphere. In particular, the scavenger may be residual magnesium in the comminuted oxidation reaction product. Finally, at least during spontaneous infiltration, the infiltration enhancer should be located in at least a portion of the filler or preform.

Under the conditions used in the process of the present invention, in the case of an aluminum / magnesium / nitrogen-spontaneous penetration system, the preform should be sufficiently permeable to allow the nitrogen-containing gas to penetrate the preform and contact the molten matrix metal. In addition, penetration of the molten matrix metal may occur in the permeable preform, causing spontaneous penetration of the molten matrix metal into the nitrogen permeable preform to form a metal matrix composite body. The amount of spontaneous infiltration and the formation of the metal matrix composite will vary according to the given combination of process conditions, e.g. the amount of magnesium nitride in the preform or filler, the presence of other alloying elements (e.g. silicon, iron, copper, manganese, chromium, zinc, and the like), the average size of the preform forming filler (e.g. particle diameter), the surface area and type of filler or preform, the penetration atmosphere the nitrogen content, the time given for the intrusion and the temperature at which the intrusion takes place. For example, by allowing infiltration of molten alumina matrix metal to occur spontaneously, aluminum can be alloyed with at least about 1 weight percent, and preferably at least about 3 weight percent 47,91833 percent magnesium (which acts as a precursor to the infiltration enhancer), based on the weight of the alloy. Other alloying elements, as described above, may also be included in the matrix metal to tailor its specific properties. In addition, additional alloying elements can affect the amount of magnesium required in the aluminum metal of the matrix so that it results in spontaneous penetration of the filler or preform. The loss of magnesium from the spontaneous system, for example due to evaporation, should not occur to such an extent that magnesium is not present to form an infiltration enhancer. Thus, it is desirable to initially use a sufficient amount of the blending elements to allow spontaneous infiltration to occur without inhibiting evaporation. In addition, the presence of magnesium in both the preform and the matrix metal, or in the preform (or filler alone), can lead to a reduction in the amount of magnesium required for spontaneous penetration (explained in more detail below).

20

The amount of nitrogen in the nitrogen atmosphere also affects the rate of formation of the metal matrix composite body. In particular, if there is less than 10% by volume of nitrogen in the atmosphere, then spontaneous infiltration 25 occurs very slowly or very little. It has been found that it is advantageous to have at least 50% by volume of nitrogen in the atmosphere, thus providing shorter penetration times due to a much higher penetration rate. The infiltration atmosphere (e.g., nitrogen-containing gas) 30 may be fed directly to the filler or preform and / or matrix metal, or may be produced as a result of decomposition of the substance.

The minimum amount of magnesium required to provide penetration of the molten matrix metal filler or preform depends on one or more factors, such as; process temperature, time, the presence of other additional alloying elements such as silicon or zinc, the nature of the filler, the presence of magnesium in one or more parts of the spontaneous system, the nitrogen content of the atmosphere, and the flow rate of the nitrogen atmosphere. Lower temperatures or shorter heating times may be used to achieve complete penetration when the magnesium content of the mixture and / or preform is increased. Likewise, the addition of certain alloying elements, such as zinc, at a given magnesium content allows the use of lower temperatures. For example, the magnesium content of the matrix metal at the lower end of the functional range, e.g., between about 1 and 3% by weight, may be used in conjunction with at least one of the following: above process minimum temperature, high nitrogen content, one or more additional alloying elements. If no magnesium is added to the preform, between about 3-5% by weight of magnesium-containing alloys are preferred due to their general applicability over a wide range of process conditions, with at least 5% by weight of 20 being preferred at lower temperatures and shorter times. Concentrations of magnesium in excess of 10% by weight may be used in the aluminum alloy to vary the temperature conditions required for penetration. The magnesium content can be reduced with other alloying elements, but these elements only serve additional functions and are used with or above the above-mentioned minimum amount of magnesium. For example, essentially no penetration occurred with nominally pure aluminum doped with only 10% silicon at 1000 ° C on a substrate 39 Crystolon (99% pure silicon carbide from Norton Co.) having a grain size of 500 mesh. However, in the presence of magnesium, silicon has been found to promote the penetration process. As another example, the amount of magnesium changes if it is fed alone to its own preform or filler. It has been found that spontaneous infiltration occurs when a lower weight percent of magnesium is fed to the spontaneous system if at least some of the total amount of magnesium fed is placed in the preform or filler, or if a higher infiltration temperature is used. It may be desirable to provide a smaller amount of magnesium to avoid the formation of unwanted metal compounds in the metal matrix composite body. With the preform being silicon carbide, it has been found that the matrix metal spontaneously penetrates the preform when the preform is contacted with the aluminum matrix metal, the preform containing at least 1% by weight magnesium and in the presence of a substantially pure nitrogen atmosphere. In the case of the alumina preform, the amount of magnesium required to achieve acceptable spontaneous infiltration is slightly higher. In particular, it has been found that when a similar aluminum matrix metal is contacted with an alumina preform, at approximately the same temperature as the aluminum that penetrated the silicon carbide preform, and in the presence of the same nitrogen atmosphere, at least about 3% to 20% magnesium may be required to penetrate spontaneously. the one obtained just in connection with the silicon carbide preform described above.

It has also been found that it is possible to spontaneously feed a penetration enhancer precursor and / or penetration enhancer to the surface of the mixture and / or preform or filler and / or preform or filler before allowing the matrix metal to penetrate the filler or preform (i.e., may not the infiltration enhancer precursor or infiltration enhancer needs to be alloyed with the matrix metal, but that it is simply fed into a spontaneous system). If magnesium were applied to the surface of the matrix metal, it may be advantageous for this surface to be the surface closest or preferably in contact with the permeable mass of the filler or vice versa; or such magnesium could be mixed with at least a portion of the preform or filler. In addition, it is possible that some combinations of surface application, doping, and placement of magnesium in at least a portion of the preform could be used. Such combinations in the application of the penetration enhancer (s) and / or the penetration enhancer precursor (s) could result in a reduction in the total weight percentage of magnesium required to promote penetration of the aluminum matrix metal preform, as well as the achievement of lower temperatures. In addition, the formation of undesired interactions of metals due to the presence of magnesium could also be minimized.

The use of one or more additional alloying elements and the nitrogen content of the surrounding gas also affect the nitration of the matrix metal at a given temperature. For example, additional alloying elements such as zinc or iron can be added to or applied to the mixture to lower the penetration temperature and thus reduce the amount of nitride formed, while increasing the nitrogen content in the gas could be used to promote nitride formation.

The concentration of magnesium in the alloy and / or applied to the surface of the alloy and / or combined with the filler or preform also tends to affect the amount of penetration at a given temperature. Similarly, in some cases where little or no magnesium may be in direct contact with the preform or filler, it may be advantageous to include at least 3% by weight of magnesium in the mixture. Alloy amounts lower than this value, such as 1 weight percent magnesium, may require higher process temperatures or additional alloying elements for penetration. The temperature required to carry out the spontaneous infiltration process of this invention may be lower: 1) when the magnesium content of the mixture alone is increased to 51,91833, e.g. to at least about 5% by weight; and / or 2) when the dopants are mixed into the permeable mass or preform of the filler; and / or 3) when the aluminum alloy contains another element such as zinc or iron. The temperature can also vary with different fillers. In general, spontaneous and progressive infiltration occurs at a process temperature of at least about 675 ° C, preferably at a process temperature of at least about 750-850 ° C. In general, temperatures above 1200 ° C do not appear to promote the process, and a range of about 675 ° C to about 1200 ° C has been found to be particularly useful. However, as a general rule, the spontaneous infiltration temperature is one that is above the melting point of the matrix metal but below the heat of vaporization state of the matrix metal. In addition, the spontaneous penetration temperature should be below the melting point of the filler. Further, as the temperature is raised, the tendency to form a reaction product between the matrix metal and the infiltration atmosphere increases (e.g., in the case of an aluminum mat-rice metal and a nitrogen infiltration atmosphere, aluminum nitride may be formed). Such cracked products may be desirable or non-desirable, depending on the intended use of the metal matrix composite body. In addition, an electric resistance month-25 operation is typically used to achieve penetration temperatures. However, any heating means which can cause the matrix metal to melt and which does not adversely affect spontaneous infiltration is acceptable for use in the present invention.

30

For example, in the present process, the permeable preform is contacted with molten aluminum in the presence of a nitrogen-containing gas (e.g., a scrubbing gas of 96% N 2 and 4% H 2) that is maintained throughout the time required for penetration. This is accomplished by maintaining a continuous flow of gas in contact with the preform and the molten aluminum matrix metal. Although the flow rate of the nitrogen-containing gas • ♦ 52 91833 is not critical, it is preferred that the flow rate be sufficient to compensate for possible nitrogen loss from the atmosphere due to nitride formation in the alloy matrix and to prevent or repel air ingress that may have an oxidizing effect on molten metal.

The method of forming the metal matrix composite can be applied to a wide variety of fillers, and the choice of fillers depends on such factors as the matrix mixture, process conditions, the reactivity of the molten matrix mixture with the filler, and the properties applied to the final composite product. When the matrix metal is, for example, aluminum, suitable fillers include a) oxides, e.g. alumina, b) carbides, e.g. silicon carbide, c) borides, e.g. aluminum dodecaboride, and d) nitrides, e.g. aluminum nitride. In a preferred embodiment, the crushed oxidation reaction product is used as a filler. In addition, the murs-20 coated oxidation reaction product can be used either alone or in combination with other fillers to provide a permeable mass or preform for penetration. If the filler tends to stick with the molten aluminum matrix metal, this can be taken into account by minimizing the penetration time and temperature or by providing an unreacted coating on the filler. The filler may comprise a substrate, such as carbon or a non-ceramic material, overlaid with a ceramic coating to protect the substrate from corrosion or deterioration. Suitable coatings 30 are e.g. ceramic oxide, carbide, boride and nitride. Ceramics useful in the present method include e.g. alumina and silicon carbide in the form of particles, flakes, fibrous crystals and fibers. The fibers may be discontinuous (in cut form) or in the form of a continuous strand 35, such as multifilament yarns. In addition, the ceramic mass or preform may be homogeneous or inhomogeneous.

53 91833

The size and shape of the filler used to form the ceramic oxidation reaction product, or the filler mixed with the crushed ceramic oxidation reaction product, can be any that is required to achieve the desired properties of the composite. Thus, the substance may be in the form of particles, fibrous supports, flakes or fibers, as the shape of the filler does not limit penetration. Other shapes can be used, such as balls, small tubes, pellets, 10 refractory nonwovens, and the like. In addition, the size of the substance does not limit the infiltration, although a mass of small particles may require a higher temperature or longer time to complete the infiltration than larger particles. In addition, the filler mass (preformed) should be permeable to penetration (i.e., it should be permeable to molten matrix metal and the penetration atmosphere).

The method of forming the metal matrix-20 si composite bodies of the present invention is not dependent on the application of pressure to press the molten matrix metal into the preform or filler mass. The invention allows the production of substantially uniform metal matrix composites having a high volume fraction of filler and low porosity because they are not dependent on the application of pressure to press the molten matrix metal into the preform or filler mass. Higher volume fractions of the filler, on the order of at least 50%, can be achieved by initially using a filler mass with a lower porosity and / or a variable size. particles to increase the efficiency of compaction. Higher volume fractions can also be obtained if the filler mass is compacted or otherwise compacted, provided that the mass is not converted to either a fully sealed closed cell pore or a completely dense structure, which would prevent the molten mixture from penetrating.

• «54 91833

It has been found that for the penetration of aluminum and the formation of a matrix around the ceramic filler, wetting of the ceramic filler with aluminum matrix metal can be an important part of the penetration mechanism. In addition, at low process temperatures, there is very little or no loss of metal to nitride conversion, resulting in a very small discontinuous phase of aluminum nitride distributed in the metal matrix. However, as the upper end of the temperature range is approached, the metal is more likely to convert to nitride. Thus, the proportion of the nitride phase in the metal matrix can be adjusted by changing the temperature at which the penetration takes place. The particular temperatures at which nitride formation becomes more significant also vary depending on factors such as the aluminum alloy of the matrix and its amount relative to the amount of filler, the amount of filler to be penetrated, and the nitrogen content of the penetration atmosphere. For example, the amount of aluminum nitride formation is believed to increase at a given process temperature as the ability of the mixture to wet the filler decreases and as the nitrogen content of the atmosphere increases.

Therefore, it is possible to customize the structure of the metal matrix during the formation of the composite so that certain properties can be imparted to the resulting product. With a given system, process conditions can be selected to control nitride formation. The composite product containing aluminum nitride has some properties that may be beneficial to or improve the performance of the product. In addition, the preferred temperature range for spontaneous penetration of the aluminum alloy may vary depending on the ceramic material used. When the filler is alumina, the penetration temperature should not exceed 1000 ° C if it is desired that the formability of the matrix 35 is not substantially reduced due to significant nitride formation. However, temperatures above 1000 ° C can be used if 91833 55 is desired to produce a composite with a matrix with lower formability and higher rigidity. Higher temperatures of about 1200 ° C can be used for penetration into silicon carbide, because when silicon carbide is used as a filler, less nitrides are formed from the aluminum alloy than when alumina is used as a filler. More importantly, when a crushed or comminuted oxidation reaction product is used as a filler, temperatures from about 750 to 850 ° C can be used from * 10

In particular, the polycrystalline material formed in the directed oxidation process may contain metallic components such as a non-oxidizing parent metal. The amount of metal can vary over a wide range from 1 to 40% by volume, sometimes even higher, depending on the wear (conversion) of the parent metal in the production of the collected or ceramic composite bodies. It may be desirable for at least a portion of the parent metal residual metal, i.e., the residue, to be separated from the oxidation reaction product before the 20 substances are used as a filler. This separation can be performed before and / or after the polycrystalline material is crushed or ground. In some cases, the oxidation reaction product may be more easily broken than the metal, and therefore in some cases it may be possible to partially separate the oxidation reaction product from the metal by grinding and screening. However, according to the present invention, the comminuted oxidation reaction product used either alone or in combination with another filler has a tendency to coalesce into a molten mixture, apparently due to a tendency to coalesce under similar process conditions and / or the presence of one or more external dopants. It has been found that this chemical tendency to coalesce results in better penetration kinetics, and correspondingly better penetration at a somewhat higher rate than in substantially the same process using a commercially available ceramic filler, i.

% · 56 9 1 8 3 3 using a filler not produced by a directed oxidation process. However, if the second filler is to be mixed with the comminuted oxidation reaction product, the comminuted oxidation reaction product should be fed in an amount sufficient to provide better penetration kinetics (i.e., at least about 10 to 25 volume percent of the filler should be comminuted oxidation reaction product). In addition, when the comminuted oxidation reaction product is used as a filler, it has been found that process 10 can be carried out at a lower temperature, which is advantageous in terms of cost and handling. Also, at lower temperatures, the molten metal does not so easily tend to react with the filler, and no undesired reaction product is formed that can have a detrimental effect on the mechanical properties of the metal matrix composite.

One factor that appears to contribute to the better penetration of the present invention is the presence of an external alloying element and / or aluminum-20 parent metal associated with the filler. For example, when alumina is formed as an oxidation reaction product upon oxidation of aluminum in air, an alloying agent is typically used in conjunction with or in combination with the aluminum parent metal, as described in the patent applications and patents mentioned at the beginning. The parent metal or dopant, or a portion thereof, may not be consumed from the reaction system, allowing it to be dispersed in a portion or substantially all of the polycrystalline ceramic. In such a case, the parent metal or alloy may condense on or on the surface of the comminuted oxidation reaction product, or the parent metal or alloy may bind to the oxidation reaction product. Without wishing to be bound by any particular theory or explanation, it is believed that when a polycrystalline material is comminuted for use as a filler, the matrix metal used to penetrate the comminuted oxidation reaction product may have a tendency to coalesce with this filler due to the base metal and / or base metal. The residual parent metal and / or alloying agents can enhance the penetration process by acting as useful external alloying elements in the final composite product; and / or act as a penetration facilitator; and / or act as a precursor to the intruder. Accordingly, the comminuted oxidation reaction product as such may provide at least a portion of the required penetration enhancer and / or penetration enhancer precursor required to effect spontaneous penetration of the matrix metal into the filler or preform.

In addition, it is possible to use a stock-15 source of matrix metal to ensure complete penetration of the filler and / or to feed a second metal having a different composition than the first source of matrix metal. In some cases, it may be particularly desirable to use a matrix metal in the storage source that differs in composition from the first source of matrix metal. For example, if the aluminum alloy is used as the first source of matrix metal, then virtually any other metal or alloy that has melted at the process temperature could be used as the stock source metal. The molten metals are often highly miscible with each other, which would result in the mixing source metal mixing with the first source of matrix metal as long as sufficient time is allowed for mixing. By using a stock source metal having a composition 30 different from the source of the first matrix metal, it is thus possible to customize the properties of the metal matrix to meet different performance requirements and thus to customize the properties of the metal matrix composite.

The blocking device can also be used in connection with the present invention. In particular, the barrier means used in the present invention may be any suitable means, 91833 58, which interacts with, prevents and stops the migration, migration or melt of the molten matrix alloy (e.g. aluminum alloy) past a defined interface. Suitable inhibiting means may be any substances, compounds, elements, compositions or the like which, under process conditions, maintain some degree of integrity and are not volatile, and which are preferably permeable to the gas used in the process, and which are also capable of locally preventing, stopping, interacting, etc., continuous penetration or any other movement past the filler interface.

Suitable barrier means include substances that the migrating molten matrix metal is substantially incapable of wetting during the process used. This type of barrier appears to have substantially no or no tendency to coalesce with the molten matrix metal, and the barrier means prevents or repels migration over the defined interface of the filler mass or preform. The inhibitor reduces the potential for 20 final machining or grinding that may be required with the metal-matrix composite product. As mentioned above, the barrier agent should preferably be permeable or porous, or it may be made permeable, for example, by drilling holes in the barrier agent or piercing it so that the gas comes into contact with the molten matrix metal.

Suitable inhibitors, which are particularly preferred with aluminum matrix alloys, are those containing 30 carbons, especially the crystalline allotropic forms of carbon known as graphite. Graphite cannot be substantially wetted under the process conditions described by a molten aluminum alloy. A particularly preferred graphite is a graphite strip product sold under the tradename Grafoil (R), 35 which is the trademark of Union Carbide. This graphite strip has sealing properties that prevent the molten aluminum alloy from passing past the defined filler interface. This graphite tape is also heat resistant and chemically inert. Grafoil (R) graphite material is flexible, durable, adaptable and flexible. It can be prepared in several forms to suit inhibitor-5 applications. However, the graphite barrier can be used as a slurry or paste or even as a paint film at or around the filler or preform interface. Grafoil (R) is considered particularly preferred because it is in the form of a flexible graphite sheet. In use, this 10 paper-like graphite is simply molded around the filler or preform.

Other preferred inhibitors for aluminum metal matrix alloys under nitrogen are transition metal borides (e.g., thi-15 danide boride (TiB2)), which molten aluminum metal alloys are unable to wet when used under certain process conditions. With this type of inhibitor, the process temperature should not exceed about 875 ° C, otherwise the effect of the inhibitor will be reduced, and in fact, at a higher temperature, penetration into the inhibitor will occur. The transition metal borides are typically in particulate form (1 to 30 micrometers). The inhibitors can be applied as a slurry or paste, preferably to the boundary surfaces of the mass of permeable ceramic filler preformed.

For aluminum metal matrix alloys, other useful inhibitors in nitrogen include volatile organic compounds that are applied as a film or layer to the outer surface of the filler or preform. Upon combustion in nitrogen, especially under the process conditions of this invention, the organic compound decomposes, leaving a carbon black film. The organic compound can be applied by conventional means such as painting, spraying, dipping, etc.

6o 91833

In addition, finely divided particulate materials can act as a barrier if penetration into the particulate material occurs at a rate that is slower than the rate of penetration into the filler.

5

Thus, the barrier agent can be applied in any suitable manner, such as by covering the defined interface with a layer of barrier means. Such a barrier layer may be formed by painting, dipping, screen printing, vaporizing, or otherwise applying the barrier means in liquid, sludge, or paste form, or by sputtering the vaporizable barrier means, or simply by depositing a solid particulate barrier layer or a layer of solid particulate barrier means, or at the interface. When the barrier means is in place, spontaneous intrusion substantially ends when the penetrating matrix metal reaches a defined interface and contacts the barrier means.

The following examples immediately contain various demonstrations of the present invention. However, these examples are to be considered as illustrative and not to be construed as limiting the scope of the invention as defined in the appended claims.

25

Example 1

Figure 1 is a cross-sectional view of an arrangement that can be used to grow an oxidation reaction product. More specifically, a rod of base metal 1, measuring 38 mm x 102 mm x 229 mm, consisting of a slightly modified Belmont Metals 380.1 aluminum alloy, was placed on a 90 grit (sieve size, grit = about 75 micrometers) E1 alumina supplied by Norton Co. bed 2, both of which were both in high purity alumina refractory boat-shaped vessel 4. The alumina vessel was obtained from Bolt Technical Ceramics and had a purity of h 61 91833 99.7%. The base metal rod 1 was placed in the E1 alumina bed 2 so that one surface of the rod 1 was approximately in line with the bed 2. Aluminum alloy 1 comprised about 2.5 to 3.5% Zn, 3.0 to 4.0% Cu, 7.5 to 9.5% Si, 0.8 to 1.5% 5 Fe, 0.2 to 0 , 3% Mg, 0 - 0.5% Mn, 0 - 0.001% Be and 0 -0.35% Sn. The aluminum alloy rod was externally alloyed by applying approximately 5 grams of 140 grit silica particles 3 substantially only to the top surface of the aluminum alloy rod 1 so that the ceramic body would grow only from the surface of the alloy 10 1 toward the atmosphere (i.e., away from the bed 2).

The vessel 4 containing the bed 2, the aluminum alloy 1 and the dopant 3 was placed in an electric resistance furnace heated to about 1100 ° C at a rate of about 200 ° C / h and held there long enough for the molten aluminum alloy 15 to react with oxygen in the atmosphere to produce an oxidation reaction product. During the heating, the air was allowed to circulate in the oven to provide the oxidant. The increased oxidation reaction product formed a "limping" on the aluminum alloy 1. Vessel 4 and its contents were then allowed to cool. The final oxidation reaction product (i.e., lump) was removed from the vessel and residual parent metal was removed by striking it with a hammer.

The oxidation reaction product was then placed in a jaw crusher and crushed into golf ball or pea sized pieces. The oxidation reaction pieces were placed in a porcelain pot with alumina powder and water. By ball grinding, the size of the pieces was reduced to smaller particles. In addition, since the oxidation reaction product 30 may contain non-oxidized residual metal from the base aluminum alloy, the pH of the solution had to be adjusted during ball grinding to reduce the potential reaction between aluminum and water. Ball grinding was continued for about 36 hours. After ball milling, the contents of the pos-35 liner were dried and sieved using conventional methods. After ball milling, all remaining pieces larger than 200 mesh were placed back into the 62 91833 ball mill and re-milled later. Particles of the crushed oxidation reaction that were less than 100 mesh and more than -200 mesh were recovered.

Figure 2 is a cross-sectional view of an arrangement that can be used to penetrate the matrix metal into the comminuted oxidation reaction product. More specifically, the comminuted oxidation reaction product 12 was placed in a high purity alumina vessel 14 similar to that used above to form the oxidation reaction product. The ingot 10 of the penetrating matrix metal was placed on top of the crushed oxidation reaction product 12 so that said matrix metal 10 extended above the surface of the comminuted filler 12. The aluminum alloy 10 used to spontaneously penetrate the crushed oxidation reaction product 12 was a matrix metal bar or ingot having dimensions of about 25 mm x 50 mm x 12 mm. The composition of the matrix metal aluminum alloy contained about 5 weight percent silicon and 5 weight percent magnesium. An alumina vessel 14 containing this arrangement of materials was placed in a muffle furnace heated by electric heaters. The muffle furnace was sealed so that essentially only penetrating gas was present. In this case, the working gas was used as the penetration atmosphere (i.e., 96 to 25% by volume nitrogen and 4% by volume hydrogen). The treatment gas was passed through the muffle furnace at a rate of about 0.35 l / minute. The muffle furnace was heated for about 10 hours until a temperature of 800 ° C was reached. The oven was kept at this temperature for about 5 hours. Oven 30 was then cooled for about 5 hours. The arrangement was then removed from the furnace and it was found that the matrix metal 10 was substantially completely surrounded by the filler 12.

Figure 3 shows a photomicrograph of the resulting metal matrix composite body 35 produced in accordance with Example 1 at 400x magnification. The darker regions 20 correspond to the crushed oxidation reaction product filler 91833 63 and the lighter regions 21 correspond to the matrix metal.

Example 2 5 This is a comparative example. In this example, a commercially available 90 grit 38 Alundum, molten alumina powder from Norton Co., was placed in a vessel. The same matrix metal as used in Example 1 was placed on top of it. The materials were placed in the same arrangement as in Example 1 shown in Fig. 2. The arrangement was placed in a muffle furnace and heated according to Example 1. After cooling, the vessel was removed and inspected. There was no significant penetration of the matrix metal in the aluminum alloy.

Example 3 This is a comparative example. In order to demonstrate that the crushed oxidation reaction product of the invention allows a lower temperature for spontaneous infiltration to occur, the following experiment was performed. The procedure of Example 2 was repeated except that a higher temperature was used. In particular, a vessel containing the material arrangement of Example 2 was placed in a muffle furnace and heated to a higher temperature of about 900 ° C according to Example 1. The oven was cooled and the vessel was removed. After inspection, it was found that substantially complete matrix metal penetration had been achieved.

The above example demonstrates that the use of a crushed oxidation reaction product as a filler is desirable. In particular, it has been found that better penetration kinetics are achieved when a crushed oxidation reaction product is used as a filler.

64 91 S33

Although the above examples have been described in detail, other variations of these examples will come to mind to one of ordinary skill in the art, and all such variations should be understood to fall within the scope of the appended claims.

10 15 20 25 30 35 li

Claims (11)

1. A process for manufacturing a metal matrix composite characterized in that as a filler, a powdered oxidation reaction product is provided and the molten matrix metal spontaneously infiltrates at least a portion of the filler using an infiltration promoting agent and / or a precursor infiltrator. means and infiltration atmosphere at least at any stage of the infiltration process. 10 Process according to Claim 1, characterized in that said powdered oxidation reaction product contains, as a seed, an infiltration-promoting agent and / or a precursor to the infiltration-promoting agent. 15 Method according to claim 1, characterized in that by means of a barrier agent, the interface surface of the filler is determined, the matrix metal spontaneously penetrating all the way to the barrier means. 20 Method according to claim 1, characterized in that the temperature during the spontaneous infiltration is higher than the melting point of the matrix metal, but lower than the evaporation temperature of the matrix metal and the melting point of the filler. 25 5. A process according to claim 1 or 2, characterized in that said powdered oxidation reaction product contains a molten base metal and at least one reaction product of either a vapor phase oxidant, liquid phase oxidizer and / or a solid oxidizer. 6. A process according to claim 1 or 2, characterized in that said oxidation reaction product contains at least one substance selected from the group consisting of aluminum oxide, aluminum nitride, silicon carbide, silicon boride, aluminum boride, titanium nitride, zirconium nitride, titanium boride, zirconium boride, zirconium boride, hafnium boride and tin oxide. 68 9 1 8 3 3 Process according to claim 1, characterized in that said oxidation reaction product is pulverized to a size range between about 200 mesh - 500 mesh. 8. Metal matrix composite piece, characterized in that it contains a three-dimensional joined matrix metal, which surrounds the filler consisting of oxidation reaction product. The metal matrix composite piece of claim 8, characterized in that at least one other filler is blended into said filler of oxidation reaction product, said at least one other filler containing at least one substance selected in the group consisting of powder, powder, powder, fiber crystals, bubbles, fibers, particles, fiber mats, broken fibers, beads, pellets, small tubes and fire resistant fabrics. Metal matrix composite piece according to claim 8, characterized in that said oxidation reaction product contains at least one substance selected from the group consisting of alumina, aluminum nitride, silicon carbide, silicon boride, aluminum boride, titanium nitride, zirconium nitride, titanium nitride, titanium nitride, titanium sodium boride and tin oxide. Metal matrix composite piece according to claim 1, characterized in that said oxidation reaction product contains at least one substance selected in the group consisting of oxides, nitrides, carbides, borides and oxinitrides. li